1. Field of the Invention
The present invention relates to a rotary ring and a mechanical seal using the same, and more particularly, to a rotary ring used for an end face type non-contact gas seal at high speed and a high speed end face type non-contact mechanical seal for gas using the same.
2. Description of the Related Art
Rotary rings used for end face type non-contact gas seals at high speed mainly comprise a hard ceramic material such as tungsten carbide, silicon carbide, silicon nitride and the like and are formed to a rectangular or substantially rectangular cross-sectional shape symmetrical with respect to right and left (refer to FIG. 8) to simplify machining and analysis.
Then, a rotary ring 31 arranged as described above is used as the rotary ring 31 of, for example, a high speed end face type non-contact mechanical seal for gas. When a rotary body (not shown) is rotated by mounting the mechanical seal on a part to be sealed, the rotary ring 31 is rotated together with the rotary body so that the seal end face 32 of the rotary ring 31 and the seal end face of a fixed ring (not shown) slide relative to each other through a subject to be sealed (inert gas, dangerous gas, air, steam, etc., hereinafter, the subject to be sealed is composed of any one of these materials), whereby the part to be sealed is sealed.
In this case, opening and closing forces, which act on both seal end faces, are balanced with each other by the cooperation of the pressure of the subject to be sealed and the urging force of an urging member (not shown) for pressing the rotary ring 31 or the fixed ring in the direction of the other of them, whereby the space between both seal end faces is kept to a space of several microns.
Since the rotary ring 31 arranged as described above is formed to a rectangular or substantially rectangular cross-sectional shape, symmetrical with respect to the right and left, the rotary ring 31 is mainly deformed in a radial direction by centrifugal force. The rotary ring therefore is not substantially deformed in an axial line direction. Therefore, it is sufficient to take deformation components due to pressure and due to heat into consideration as the deformation components of both the rings which affect the pressure distribution therebetween.
In this case, the deformation due to pressure can be optionally controlled by a buoyancy generating means 34 which is composed of dynamic pressure slits, static pressure slits, taper portions, stepped portions and the like formed at the seal end faces 32. However, the deformation due to heat can not be completely eliminated and it is difficult to reduce the deformation to a negligible level so long as a high speed seal is concerned.
While heat is generated from the respective surfaces of rotary components, it is generated in a highest density from the seal end face 32. As a result, a temperature gradient, which is high on the side of the seal end face 32 and low on the side of the anti-seal end face 33, is produced in the interior of the rotary ring 31. The temperature gradient thus causes the seal end face 32 to exhibit convex deformation by which the inner peripheral side thereof is swelled.
In many cases, the convex deformation increases the opening force generated between both the seal end faces, thereby increasing an amount of leakage of the subject to be sealed from between both seal end faces. On the contrary, however, there is also a case that the space near to the outer peripheral portion of the rotary ring 31 where the dynamic pressure slits exist is increased and a hydraulic pressure action is weakened. Thus a danger exists that the inner peripheral portion of the rotary ring 31 will come into contact with an opposite member.
In a dynamic pressure type non-contact seal, there is such a fundamental characteristic that a higher number of revolutions results in a higher dynamic pressure action so that the space between both the seal end faces is increased. However, when the affect of deformation due to heat is relatively increased on the dynamic pressure action, a problem arises in that the subject to be sealed is leaked in an excessive amount and the inner peripheral portion of one of the seal end faces comes into contact with the other of them.
The influence of the deformation due to heat is relatively increased in such a case that a slight amount of inclination of the rotary ring 31 causes the inner peripheral portion thereof to come into contact with the opposite member because the seal end face 32 has a large width, that is, because the size obtained by subtracting the inside diameter of the rotary ring 31 from the outside diameter thereof is large as well as a case that the deformation due to heat is made in a large amount due to the characteristic of a material.
An object of the present invention, which solves the problems of the conventional mechanical seal, is to provide a rotary ring and a mechanical seal using the rotary ring to reliably prevent a subject to be sealed from leaking excessively such that the inner peripheral portion of the rotary ring comes into contact with an opposite member even if the influence of deformation due to heat is relatively increased on a dynamic pressure action.
To solve the above problems, the present invention employs a rotary ring which is annular and has a center of gravity located at the center of a plate thickness comprising a seal end face located at an end of the rotary ring in the axial line direction thereof perpendicularly to the axial line, the seal end face sliding on the seal end face of a fixed ring through a subject to be sealed; and an anti-seal end face located at the other end of the rotary ring perpendicularly to the axial line, wherein the cross sectional shape of the rotary ring is formed such that the center of gravity is located at a position nearer to the anti-seal end face than the center of the plate thickness. The present invention employs such a cross sectional shape of the rotary ring made asymmetric with respect to the right and left by locating the center of gravity of the rotary ring at the position nearer to the anti-seal end face than the center of the plate thickness by forming a stepped portion, a recessed portion, an inclining portion and the like around the outer peripheral portion of the rotary ring. The present invention employs such a rotary ring comprising a material obtained by hardening at least a portion of a simple metal, a simple resin, a metal material, or a resin material by a means such as coating, plating, spraying, vapor deposition, nitriding and so forth. The present invention employs a mechanical seal comprising an annular rotary ring mounted on a rotary body so as to rotate integrally with the rotary body, having a seal end face located at an end of the rotary ring in the axial line direction thereof perpendicularly to the axial line, an anti-seal end face located at the other end of the rotary ring perpendicularly to the axial line and a center of gravity located at the center of a plate thickness; an annular fixed ring mounted on a fixed body, having a seal end face located at an end of the fixed ring in the axial line direction thereof perpendicularly to the axial line, the seal end face sliding on the seal end face of the rotary ring through a subject to be sealed; and an urging member for pressing the rotary ring or the fixed ring in the direction of the other thereof, wherein a predetermined space is kept between the seal end face of the rotary ring and the seal end face of the fixed ring by balancing closing forces with opening forces by the cooperation of the pressure of the subject to be sealed and the urging force of the urging member, and the cross-sectional shape of the rotary ring is formed such that the center of gravity thereof is located at a position nearer to the anti-seal end face than the center of the plate thickness. The present invention employs a cross sectional shape of the rotary ring made asymmetric with respect to the right and left by locating the center of gravity at the position nearer to the anti-seal end face than the center of the plate thickness by forming a stepped portion, a recessed portion, an inclining portion and the like around the outer peripheral portion of the rotary ring. Further, the present invention employs a rotary ring comprising a material obtained by hardening at least a portion of a simple metal, a simple resin, a metal material, or a resin material by a means such as coating, plating, spraying, vapor deposition, nitriding and so forth.
Since the present invention employs the above means, a large amount of centrifugal force can act on the anti-seal end face, and thus concave deformation can be made to the seal end face by the centrifugal force. Accordingly, the convex deformation made to the seal end face due to heat can be cancelled by the concave deformation.